The present invention relates to a technique of performing a temperature calibration in an infrared imaging device, and a technique of displaying an infrared image in a more legible manner.
An infrared imaging device is capable of remotely measuring the temperature of an object, and is used as a surveillance camera, or the like, for detecting a human or detecting a car.
FIG. 9 is a diagram illustrating an exemplary configuration of a conventional infrared imaging device (described in Japanese Laid-Open Patent Publication No. 5-302855). The configuration of FIG. 8 is used for the purpose of calibrating the relationship between the output signal and the temperature.
In FIG. 8, the characteristics of an infrared detector 1010 (object temperature versus brightness table) as illustrated in FIG. 9 are pre-stored in temperature characteristic correction means 1050. Each of graph curves 1210, 1220, 1230 and 1240 of FIG. 9 represents a relationship between an object temperature T and an output voltage Ei of the infrared detector 1010, with temperatures T1, T2, T3 and T4 in the vicinity of the infrared detector 1010 being used as parameters.
Temperature measurement means 1080 measures a temperature Tx in the vicinity of the infrared detector 1010. Temperature characteristic correction means 1050 uses the temperature Tx and the characteristics of FIG. 9 to obtain the object temperature T from the output voltage Ei of the infrared detector 1010. Assuming that T2 less than Tx less than T3, the temperature characteristic correction means 1050 creates a characteristic curve 1250 by interpolating the graph curves 1220 and 1230, respectively corresponding to the temperatures T2 and T3, and converts the output voltage Ei of the infrared detector 1010 into the object temperature T by using the characteristic curve 1250.
FIG. 10 is a diagram illustrating another exemplary configuration of a conventional infrared imaging device (described in Japanese Laid-Open Patent Publication No. 10-111172).
In FIG. 10, optical systems 1310 and 1320 cause the infrared image of an object 1330 to form an image on an infrared detector 1340. Each of a reference heat source A 1350 and a reference heat source B 1360 is a heat source using a Peltier element, and the temperature thereof is variable and controlled by controllers 1440 and 1450, respectively.
The infrared imaging device illustrated in FIG. 10 images the target object during an effective scanning period, while it images the reference heat source A 1350 and the reference heat source B 1360 during an ineffective scanning period. Average value calculation means 1370 calculates the average value of the output of the infrared detector 1340 during the effective scanning period. Reference heat source A output calculation means 1380 calculates the average value of the output of the infrared detector 1340 while imaging the reference heat source A 1350 during the Ineffective scanning period, whereas the reference heat source output calculation means 1390 calculates the average value of the output of the infrared detector 1340 while Imaging the reference heat source B 1360 during the ineffective scanning period, and median value output means 1400 outputs the median value of these calculation results. A subtractor 1410 subtracts the output of the median value output means 1400 from the output of the average value calculation means 1370, and an adder 1420 adds a predetermined temperature difference xcex94T to the subtraction result and provides the obtained value to the reference heat source A controller 1440, whereas a subtractor 1430 subtracts the temperature difference xcex94T from the subtraction result and provides the obtained value to the reference heat source B controller 1450. The controllers 1440 and 1450 perform a feedback control so that the subtraction result of the subtractor 1410 is zero, i.e., the output of the average value calculation means 1370 and the output of the median value output means 1400 are equal to each other.
With such a control, even if the scene being imaged changes, the temperatures of the reference heat source A 1350 and the reference heat source B 1360 change according to the average value of the temperature of the obtained image, and are always controlled within a predetermined temperature range (average value xcex94t). Correction means 1460 obtains a correction coefficient used for correcting output variations, based on the output of the infrared detector 1340 while imaging the reference heat source A 1350 and the reference heat source B 1360 during the ineffective scanning period. In this way, a temperature calibration suitable for the temperature range to be measured is realized.
FIG. 11 is a diagram illustrating another exemplary configuration of a conventional infrared imaging device (described in Japanese Laid-Open Patent Publication No. 10-142065). The configuration of FIG. 11 is used for the purpose of eliminating two-dimensional output variations.
In FIG. 11, first shutting means 1510 is provided for shading correction, and second shutting means 1530 is provided for inter-pixel output variation correction. During an imaging operation, the first and second shutting means 1510 and 1530 are open, whereby an infrared radiation coming through an optical system 1520 forms an image on an infrared detector 1540.
The first shutting means 1510 is closed by a control means 1560 once in every 30 seconds so as to shut off the infrared radiation. In this state, inter-pixel output variation correction means 1550 determines a shading correction value based on the output of the infrared detector 1540. On the other hand, the second shutting means 1530 is also closed by the control means 1560 once in every 30 seconds so as to shut off the infrared radiation. In this state, the inter-pixel output variation correction means 1550 determines a sensitivity correction value based on the output of the infrared detector 1540.
In order to obtain, with a good precision, the temperature information of the object by using an infrared imaging device, it is necessary to perform two types of image correction. One is a so-called xe2x80x9ctemperature calibrationxe2x80x9d, i.e., a calibration of the relationship between the output signal (brightness signal) and the temperature, and the other is a correction of two-dimensional output variations in the image.
Possible factors necessitating the temperature calibration include changes in characteristics due to changes in the temperature of the infrared detector itself, fluctuations in the amount of infrared radiation from an optical system such as a lens or a lens barrel due to changes in temperature, etc. For example, when an infrared imaging device is used outdoors, there are violent temperature changes, whereby even immediately after a temperature calibration, the correspondence between the temperature and the brightness shifts from the actual values, thereby reducing the, legibility of the image. Moreover, when it rains, the brightness level substantially decreases for the same object being imaged due to a temperature decrease.
There are two factors for two-dimensional output variations. One is sensitivity variations among various pixels of an infrared detector, and non-uniformities are introduced to the surface of an infrared image by such sensitivity variations. The other is what is called xe2x80x9clens shadingxe2x80x9d, which is a phenomenon wherein the amount of light received by a central portion of the infrared detector is uniformly higher than that received by a peripheral portion thereof, due to the nature of the optical system.
In the conventional example of FIG. 8, the temperature in the vicinity of the infrared detector 1010 is measured, and an object temperature versus brightness table is referenced based on the vicinity temperature. However, in the case of imaging with an infrared imaging device being installed outdoors, for example, the temperature of an optical system 1020 is substantially different from the temperature in the vicinity of the infrared detector 1010, whereby the amount of infrared radiation from the optical system 1020 during an imaging operation is substantially different from that-when the table is created. As a result, it is not always possible to realize a high precision temperature compensation.
In the conventional example of FIG. 10, the heat sources serving as references for the temperature calibration are provided between the optical systems. Therefore, in the case of imaging with an infrared imaging device being installed outdoors, for example, there are violent fluctuations in the temperature of the optical systems, and the calibration cannot be performed with the influence of the fluctuations in the temperature of the optical systems being taken into consideration. Particularly, the fluctuations in the infrared radiation from the optical system 1310 on the outer side with respect to the heat sources are substantial, thereby fluctuating, the apparent measured temperature of the object.
Moreover, the conventional example of FIG. 11, despite the complicated configuration with two shutting means, can only correct two-dimensional output variations, and cannot calibrate the relationship between the output signal and the temperature. Moreover, since the timing at which to perform a correction is fixed, it is not suitable for use as a surveillance camera, or the like, because there are periods during which an imaging operation cannot be performed.
As described above, conventional infrared imaging devices have not necessarily succeeded in realizing a high precision image correction. Particularly, serious problems arise when they are used under environments with violent changes such as when they are installed in a vehicle.
An object of the present invention is to provide an infrared imaging device with a simple structure capable of realizing an image correction with a higher precision than in the prior art.
Specifically, the present invention provides an infrared imaging device, including: an infrared detector; an optical system for causing an infrared radiation from an object to form an image on the infrared detector; shutting means configured so that the shutting means can be opened/closed and so as to shut off an infrared radiation coming into the optical system when the shutting means is closed; and correction means for correcting an output of the infrared detector, wherein the correction means determines a correction coefficient for correcting fluctuations in an amount of infrared radiation from the optical system by using an output of the infrared detector imaging the shutting means while the shutting means is closed.
According to the present invention, the shutting means is provided for shutting off, when it is closed, the infrared radiation coming into the optical system, and the correction coefficient for correcting the fluctuations in the amount of infrared radiation from the optical system while the shutting means is closed. Therefore, it is possible to perform a correction with the fluctuations in the radiation from the optical system being taken into consideration. Therefore, it is possible to realize an image correction with a higher precision than in the prior art.
It is preferred that the correction means in the infrared imaging device according to the present invention determines a second correction coefficient for correcting variations in a DC offset among pixels and fluctuations in an amount of infrared radiation from the optical system by using the output of the infrared detector imaging the shutting means being closed and a first correction coefficient proportional to a sensitivity of each pixel of the infrared detector and shading.
It is preferred that the infrared imaging device includes second shutting means configured so that the second shutting means can be opened/closed and so as to shut off an infrared radiation coming into the optical system when the second shutting means is closed; and the correction means determines the first correction coefficient by using the output of the infrared detector imaging the shutting means being closed and an output of the infrared detector imaging the second shutting means being closed.
It is preferred that the infrared imaging device includes temperature setting means for setting a temperature of the shutting means; and the correction means determines the first correction coefficient by using an output of the infrared detector imaging the shutting means being closed, which has been set to a first temperature by the temperature setting means, and an output of the infrared detector imaging the shutting means being closed, which has been set to a second temperature by the temperature setting means.
It is preferred that the infrared imaging device according to the present invention includes temperature measurement means for measuring a surface temperature of the shutting means; and the correction means determines the correction coefficient by using a temperature measured by the temperature measurement means.
It is preferred that the optical system in the infrared imaging device according to the present invention is set to a non-focused state while the shutting means is closed.
It is preferred that the shutting means in the infrared imaging device according to the present invention is a flat-plate member having a uniform temperature distribution.
It is preferred that the infrared imaging device according to the present invention includes temperature setting means for setting a temperature of the shutting means; and the temperature setting means sets the temperature of the shutting means to a temperature in a vicinity of a temperature of a particular object to be imaged while the shutting means is closed.
The present invention also provides an infrared imaging device to be installed in a moving, object, the infrared imaging device including: an infrared detector; correction means for correcting an output of the infrared detector; and control means for controlling a timing at which the correction means determines a correction coefficient based on a signal sent from at least one of the following means provided in the moving object: means for detecting a speed of the moving object; means for identifying a traffic signal of a traffic light located in a traveling direction of the moving object; and means for determining presence/absence of an object to be detected in the traveling direction of the moving object.
According to the present invention, when the infrared imaging device is installed in a moving object, the timing at which to determine the correction coefficient is controlled based on at least one of the following: the speed of the moving object; the traffic signal of the traffic light located in the traveling direction of the moving object; and the presence/absence of an object to be detected in the traveling direction of the moving object. Therefore, it is possible to determine the correction coefficient at appropriate timings.
The present invention also provides a vehicle having the infrared imaging device according to the present invention, the vehicle including means for detecting a speed of the vehicle, wherein the control means provided in the infrared imaging device receives an output signal of the speed detection means to control the timing at which to determine the correction coefficient. Alternatively, the vehicle includes means for identifying a traffic signal of a traffic light located in a traveling direction of the vehicle, wherein the control means provided in the infrared imaging device receives an output signal of the traffic light identification means to control the timing at which to determine the correction coefficient. Alternatively, the vehicle includes means for determining presence/absence of an object to be detected in a traveling direction of the vehicle, wherein the control means provided in the infrared imaging device receives an output signal of the object determination means to control the timing at which to determine the correction coefficient.
The present invention also provides an infrared imaging device to be installed in a vehicle, the infrared imaging device including an infrared detector; an optical system for causing an infrared radiation from an object to form an image on the infrared detector; and a temperature retaining structure for stabilizing a temperature in a vicinity of the infrared detector and the optical system by using a mechanism in the vehicle.
According to the present invention, when the infrared imaging device is installed in a vehicle, the temperature in the vicinity of the infrared detector and the optical system is stabilized by the temperature retaining structure using a mechanism in the vehicle. In this way, fluctuations of the image quality are suppressed.
It is preferred that the temperature retaining structure circulates an engine coolant of the vehicle in the vicinity of the infrared detector and the optical system.
The present invention also provides a vehicle, including: an infrared imaging device; and a temperature retaining structure for stabilizing a temperature in a vicinity of the infrared imaging device by using a mechanism in the vehicle.
It is preferred that the temperature retaining structure circulates an engine coolant of the vehicle in the vicinity of the infrared imaging device.
The present invention also provides an infrared imaging device to be installed in a vehicle, the infrared imaging device including a mechanism for setting/changing a imaging direction of the infrared imaging device, wherein the mechanism sets the imaging direction toward outside of the vehicle during a normal operation, and sets the imaging direction toward a part of the vehicle, which is to be a temperature reference, during a calibration operation.
The present invention also provides a vehicle, including: an infrared imaging device; and a mechanism for setting/changing a imaging direction of the infrared imaging device, wherein the mechanism sets the imaging direction toward outside of the vehicle during a normal operation, and sets the imaging direction toward a part of the vehicle, which is to be a temperature reference, during a calibration operation.
With such configurations of the present invention, an infrared imaging device installed in a vehicle can calibrate temperature characteristics without providing a special temperature reference.
The present invention also provides an infrared image adjustment device for adjusting a display temperature range of an infrared image, including: first means for detecting, from the infrared image, an upper limit and a lower limit of a temperature range suitable for displaying the infrared image; second means for storing a predetermined temperature based on a particular object to be imaged; and third means for setting the display temperature range so as to include at least the predetermined temperature, based on the upper and lower limit temperatures detected by the first means and the predetermined temperature stored in the second means.
According to the present invention, since the predetermined temperature based on the particular object to be imaged is included in the display temperature range, the display brightness of the infrared image does not fluctuate even in cases where the object to be imaged appears and disappears in the obtained image. Therefore, it is possible to display a stable image, whereby a detailed classification operation, or the like, using an infrared image pattern can be realized.
In the infrared imaging device according to the present invention, the second means stores, as the predetermined temperature, an upper limit and a lower limit of a temperature range based on the particular object to be imaged; and the third means sets, as an upper limit of the display temperature range, a larger one of the upper limit temperature detected by the first means and the upper limit temperature stored in the second means, while setting, as a lower limit of the display temperature range, a smaller one of the lower limit temperature detected by the first means and the lower limit temperature stored in the second means.
The first means in the infrared imaging device according to the present invention detects a highest temperature and a lowest temperature among temperatures indicated by the infrared image as an upper limit and a lower limit, respectively, of the temperature range.